1. Field of the Invention
The present invention relates to a liquid jet recording apparatus, a liquid jet head unit, and a liquid jet recording method.
2. Description of the Related Art
Conventionally, as an apparatus for jetting liquid toward a recording medium, a liquid jet recording apparatus for jetting a droplet from a plurality of nozzles toward a recording medium is known. As such a liquid jet recording apparatus, for example, one having a liquid jet head mounted thereon for jetting toward a recording medium a droplet of several to several ten picoliters is known. A liquid jet head which jets such a minute droplet is adapted to control liquid in the nozzle so as to be optimum for being jetted in order to materialize satisfactory jetting of the liquid. Here, a state of liquid which is optimum for being jetted is a state in which the pressure of the liquid in the nozzle is a negative pressure and a meniscus is formed in the nozzle. In order to make such a pressure adjustment, an apparatus is known in which a pump or an air valve is provided in a flow path of liquid between a liquid container and a liquid jet head for adjusting the pressure.
Japanese Patent Application Laid-Open No. 2005-34999 describes an ink jet printer including a pump for depressurizing liquid in a nozzle of a liquid jet head, an air communication valve for pressurizing liquid in the nozzle of the liquid jet head, a pressure sensor for measuring the pressure of liquid in the nozzle of the liquid jet head, and a control portion for operating the pump and the air communication valve based on a measured value by the pressure sensor. In the ink jet printer, the pressure of liquid to be supplied to the nozzle is adapted to be increased or decreased by the pump and the air communication valve disposed in a liquid flow path from an auxiliary tank for storing liquid to the liquid jet head.
However, the ink jet printer described in Japanese Patent Application Laid-Open No. 2005-34999 has a problem that, both the pump and the air communication valve are necessary for increasing and decreasing the pressure of the liquid in the nozzle, and hence the structure of the apparatus is complicated.
Further, as an ink jet printer in recent years, a large printing apparatus which can print a large area of a surface of a poster or a signboard is often used, and there is a tendency to enlarge the apparatus in a specific field. In such a large printing apparatus, compared with a case of a small printing apparatus, the distance from a liquid container for storing liquid to be jetted to a liquid jet head is larger, and thus, the length of a flow path for supplying the liquid to the liquid jet head is larger. Therefore, in a large apparatus, the loss of pressure on the liquid in the flow path increases, and the liquid may be prevented from being supplied to the liquid jet head with the pressure thereon being held appropriate for the liquid jet environment. In order to precisely set the pressure value of liquid in the liquid jet head, it is necessary to precisely measure the pressure value in the liquid jet head and to supply the liquid with appropriate pressure thereon being held.
Further, when a carriage including a liquid jet head scans a range to be printed, the position of a flow path for communicating a liquid container with the liquid jet head repeatedly changes as the carriage moves, and hence liquid existing in the flow path is under a pressure load. In this case, liquid affected by the pressure load is supplied to the liquid jet head which is located downstream from the flow path, and thus, it is difficult to hold the appropriate pressure for the liquid jet environment. Normally, such a pressure load on liquid is reduced by a pressure damper (liquid storing portion), however, pressure loss due to the increased length of the flow path still affects the liquid, which prevents materialization of an appropriate printing environment.
Further, as the range to be printed increases as described above, the range to be scanned by the carriage including the liquid jet head also increases, and thus, liquid having the amount beyond the ability of the pressure damper to decrease the pressure load may be supplied to the liquid jet head, and thus, deterioration of the printing environment is expected as the apparatus becomes larger.
As described above, in order to prepare a sophisticated printing environment for a printer, it is an urgent necessity to precisely measure and grasp the pressure of liquid in the liquid jet head.